Electric control system



March 22, 1938. w. F. EAMES ELECTRIC CONTROL SYSTEM Filed June 26,

l NEmoR J vllww Z T {WA/ LW Dn Rlllllll Ill-III ATT Patented Mar. 22, 1938 f UNITED STATES PATENT ori-ICE ELEc'rmc coN'rnoL sYs'rEM William F. Eames, Pittsburgh, Pa., assigner to vWestinghouse Electric Elevator Company, Chicago, Ill., a corporation of Illinois Application June 26, 1986, Serial No. 87,361

llClaims.

My invention relates to systems for controlling the operation of electrical apparatus, andmore particularly to variable voltage systems of control in which direct current motors are operated by the voltage supplied to them from separately excited generators.

In systems of this character (usually known as the Ward Leonard type), the starting, the stopping, the reversing and the speed of the motor are controlled by controlling and varying the excitation of a eld winding on the generator. When such systems are provided for operating elevators, hoists, planers and 'similar machinery and apparatus the motor is usually designed to provide a constant speed regardless of load. A characteristic of this kind of system is that the motor starts sometimes somewhat more slowly than is desired, particularly in the operation of elevators. It is noticeable in the ordinary startng ofthe elevator car on a trip between oors, and it is very noticeable in leveling operations to bring the car accurately level with a floor when a stop is being made. Some diiculty is occasioned by the residual magnetism in the generator. For instance when the car is being reversed in a leveling operation at a iloor the residual magnetism causes the vstarting of the generator to be slower than when starting in the original direction.

Therefore, it is an object of my invention to provide a control system in which the motor will start quickly and, when used in an elevator sys-- tem will prevent undue delay in starting the car and also enable it to beleveled quickly and accurately at .a oor.

Another object of my invention is to provide for compensating for the residual magnetism in the generator, when starting the motor, and also to provide for compensating for the residual magnetism with one value when starting the motor in the same direction as that in which it has been operating and with another value when starting the motor in a direction reverse to that in which it has been operating, so as to secure practically the same rate of acceleration in each case.

In order to attain these objects, I provide a control system'including a small auxiliary direct current dynamo-electric machine which operates as an idling motor while the main motor is stopped, but which is disconnected from its source of energy and temporarily acts as a generator, by reason of itsinertia, to supply a boosting current to the auxiliary generator eld winding when themain motor starts. The system also includes novel connecting arrangements for so connecting the dynamo-electric machine in the system that it will always be running and ready for use as a forcing generator when the main motor is started and will compensate for the resid- 5 ual magnetism in the generator in accordance with the forward or reverse starting of the main motor after a stop.

For a better understanding of the invention, reference may be had to the accompanying draw- 10 ing in which:

Figure 1 is a diagrammatic representation of a control system embodying my invention as applied to an elevator system and is drawn in what is known as'the straight-line" style; and

Fig. y2 is a representation of the relays embodied in Fig. 1.

'I'he illustration of the relays in Fig. 2 shows them with their coils and contact members disposed in horizontal alinement with their positions in the straight-line circuits of Fig. 1, so that the reader may readily determine the identity of any relay, the number and kind of its contact members, and the position of its coil and its contact members in the straight-line circuit.

Referring more particularly to the drawing, an elevator car C is illustrated as suitably suspended in a hatchwayy (not shown) by a cable Il which passes over a hoisting drum I2 to a counterweight I3.

Thehoisting drum. I2 is disposed on a shaft Il driven byan elevator motor I5. The motor I5 is provided with an armature ISA and a separately excited shunt eld winding ISF.

A variable voltage system of control is provided for operating the elevator motor I5 wherein the armature ISA of the elevator motor is connected in loop circuit with the armature GA of a generator G. 'Ihe generator G is provided with a series ileld winding GSF and a separately excited fleld winding GF.

The armature GA of the generator G is driven by means oi a main driving motor II whichincludes a squirrel cage rotor I8 and a three-phase, star-connected stator winding I 9. The outer leads of the stator winding may be connected to any suitable source of electrical energy represented by the supply conductors LI, L2, and L3.

A direct current exciter E having a shunt field winding EF and an armature E is disposed on the shaft 20 of the driving motor for providing a direct current source of excitation for building up the excitation of the generator eld winding. GF at a predetermined rate and then maintain- 65 ing it at a predetermined value, for energizing the field winding I5F of the elevator motor and for supplying the control circuit of the elevator rep- -resented by the conductors L+ and L- with suitable energy for operating the various control switches, relays, etc.

'I'he direction of the excitation current for the field winding GF of the generator may be suitably controlled by means of an up direction switch U and a down direction switch D. 'Ihe value oi' the current supplied to the field winding GF may be controlled by a resistor TI which may be controlled through a high speed relay V.

A car switch CS is provided for the car C for controlling the up and the down direction switches U and D in operating the elevator motor to start and stop the car- C. 'Ihe car switch 1s provided with oontoot points n and n which control the up direction and the down direction switches and with contacts 24 and 2B which control the high speed relay V.

`An automatic leveling system is provided for causing the car to level itself with the floor il it overruns or underruns the door level when a stop is being made at a landing. The leveling apparatus is old and well known in the art, and is here shown as represented by a leveling switch LS having a pair of up contact members LSI disposedtobeoperatedbyaswitcharmll engaging the upper face of a-'cam 3l when the car stops just below the door, and a pair of down contact members LS! disposed to be operated by a lever Il engaging the lower face of the cam 3| when the car stops above the iioor. Normally the levers ll and I3 are held in a retiring posi tion by a retiring coil Il when the car is the various floor landings (not shown) but which permits the levers to fall into operating position for leveling the car at a door whenever the car is stopped at that iloor. When the car stops just below a iioor. the cam Il causes the lever Il to close the contact members LSI and thereby energizes the up direction switch to cause the car to move upwardly. When the car stops above a door, the lever Il is operated by the cam 3| to close the contact members LS! and thereby energiaes the down direction switch to move the car downwardly until it is level with the floor, when the lever il slides oi! the cam 3|, thus opening the contact members LS2 and stopping the car.

In systems of this character, it is desirable to have the elevator motor start quickly for any normal run and also for the leveling of the car at a iloor whenever a leveling operation is n. In order to accomplish this, I have provided a iield forcing means by which the ileld current in the auxiliary field winding GF of the generator G is increased or booned for a very short period at the instant the direction switch is closed to start the car inresponse to the leveling device.

The ileld forcing means includes a small frame direct current dynamo electric machine M which acts as an auxiliary motor or. generator, in accordance with the manner in which it is con- -nectedinthesystenn Normallythedynamold is connected across the control circuits so that it idly rotates as a motor whilerthe car is nmning or standing. However, when the elevator motor istobestartedafterastop.thedynamoMisdis connected from the control circuit and connected to the generator field GF. Its tendency to keep on rotating then causes it to act as a generator to supply a forcing or boosting current to the main generator for the short riod it keeps on `running under its own inertia afterbeing cut oil' from its power. 'I'he dynamo M is provided with an armature A which is normally connected across the supply conductors L+ and L- through a current limiting resistor r3. The dynamo M is also provided with a field winding MS which is connected. for constant excitation through a resistor rl and a hand 3l, across the conductors L+ and L The stored energy of the dynamo may be varied by moving the hand 3l on the resistor rl to control its speed.

The motor M may be of any suitable size. The system here illustrated usually employs a voltage of approximately 240 volts on its control conductors and a motor of about 300 watts capacity will be found satisfactory in most cases.

A regulatingv or voltage-responsive relay R is provided for eifectingthe disconnection o! the .dynamo M from the generator field when its boosting voltage falls below a predetermined value. The relay R should be so constructed that it will be energized when the electrical energy impressed upon it amounts to a predeterminedl value and will be deenergized when the voltage across it drops below a predetermined value. In the present case, the relay R is designed for energization at about 150 volts and deenergisation at about 20 volts. The present values are given as an example of suitable values but the-relay may be designed to operate at any other suitable voltages.

' A eld forcing connecting relay T is provided for effecting the disconnection of the dynamo H from the supply conductors L+ and L'- while operating as a motor and for connecting it to the auxiliary ield winding GF of the generator G to act as a generator in boosting the current in the eld winding GF, when the elevator motor 'is to be started. A re-set relay S is provided for resetting the system to cause the auxiliary motor M to again start in operation. after it has served as a boosting generator.

In addition to providing a forcing current for the generator. it is also desirable to control the forcing current in accordance with the residual magnetism in the generator ileld after a stop has beenmade so that a predetermined value of forcing current wilibe provided when the motor is to resume operation in the same direction and a higher predetermined value of forcing current will be provided when the motor is to resume operation in a reverse direction. A down direction preference relay FD, an up direction preference relay PU and a compensating relay X are provided for this m1111088.

It is believed that the invention may be best understood by an assumed operation of the system illustrated in the drawing.

It will be assumed that the car is on an up trip and that the main line switches Il have been closed to render the control' system operative. The closing of the switches Il energizes the exciter E, the field winding ISF of the motor Il, the armatureA and theiieldwindingMSofthedynamo M. the regulating relay R, the re-setting relay S and the up direction preference relay PU. Hence the motor immediately starts operating as an idling motor.

It will be assumed that the car attendant is desirous of operating the car upwardly and rotates the car switch CS in the counter-clockwise direction. The engagement of the switch CS with its contact member 3l energises the retiring coil I5 of the leveling switch LS and thereby withdraws the levers lll and 33 from being operated by theengagement ofthecam 3l at anyiloorso members T2 and closed its contact members Ti.

The continued movement vof the switch CS to engage its. contact member 23 energizes the. up direction switch U by a circuit extending from supply conductor L+ through CS, 23, U, to L This causes the elevator car to start upwardly. The energized switch U closes its contact members UI thereby energizing the brake coil 6 to release the brake 5 and permit the operation of the hoisting drum I2. The closing of the contact members U2 and U3 energizes the field winding GF of the generator G to effect upward operation of the car by a circuit extending from the supply conductor L+-through U2, GF, U3, rl to L As the car switch is moved further to engage the contact member. 25, it thereby energizes the high speed relay V to close its contact members VI thus eliminating the eect of the resistor rl in the circuit of the auxiliary eld WindingGf and causing the elevator to run at its high speed.

As previously indicated, the dynamo electric machineM was connected and running as a motor at the time the car switch was thrown to its on position. At the instant the car switch U was. energized it closed its contact members U4 and thereby energized the field forcing connecting relay T. This circuit extended from the supply conductor L+ through U4, SI, T, L .l The energ'izing relay T immediately opened its contact The opening of the contact members T2 disconnected the armature A of the dynamo M from the supply conductors L+ and L and the closing of the contact members TI connected the armature A of the dynamo to the circuit through the iild winding GF of the generator G. Therefore the dynamo M then ceased receiving energy from the supply conductors L+ and L but its armature A was connected to the generator held.

windings GF and its inertia caused it to continue rotation for a short period of time during which time it operated as a generator supplying a boosting or forcing current to the generator. At the instant the motor M was connected across the main generatoreld, it had a counter E. M. F. suilcient to deliver energy to the generator field at full voltage. As the energy was delivered by the dynamo, its speed dropped and its voit-age also, but it delivered suillcient current to force or boost the generator field to such an extent as to cause the car to start more quickly than it would have started without thev operation oi the dynamo.

As the speed of the dynamo M dropped, the voltage across the regulating relay R. also dropped and, as it reached say, approximately volts, the relay R became deenergized and opened its contact members RI and R2. The opening of the contact members R2 deenergized the re-setting relay S which in turn opened its contact members SI and thereby deenergized the iicld forcing connecting relay T. The deenergized relay T now opened its contact members Tl and closed its contact members T2, thereby disconnecting the auxiliary motorM from the auxiliary field winding GF but at the same time connecting it across the supply conductors L+ and L and thereby causing it to again start in rotation, readyfor the next starting operation.

It may be noted here that my use of the dynamo M is so arranged that it is always in full operation at the time any starting operation is to be effected, so that it is capable of delivering its boosting current the instant the direction switch closes its contact members for energizing the generator field in starting thecar, either in a landing operation or in a normalcar starting operation.

When the up direction switch U was energized, f the closing of itscontact members U1 energized the residual compensating rela X by a circuit extendingv from supply conductor L+ through PU3, U1, X, L The energized relay X thereupon opened its contact members Xl, thus causingv the forcing current from the dynamo M tov ilow through the resistor r2 in moving to the generatory eld GF. This resistance r2 compensated for the residual magnetismin the generator eld in that it prevented the supply of as large a forcing current as would have been supplied if the relay T had vnot been energized. The

Amount supplied'was sufficient however as the generator was simply resuming operation in the same direction as that in which it had been operating. Hence it is seen thatV the use of the relay X as connected in the manner described along with the direction relays PD and PU provides for controlling the amount of boosting cur- .rent in accordance with whether the generator is starting in the vsame direction or is being reversed.

As the car approaches the floor at which a stop is to be made the car attendant centers the car switch CS, thereby iirst 'deenergizing the high speed relay V to reinsert` the resistor rl in the circuit for the iield winding GF to reduce the speed of the car vand then deenergizes the up direction relay U which opens its contact members U1, thereby deenergizing the .compensating relay X and closes its contact members U5, thereby energizng the resetting relay S to prepare the connecting relay T to be again operated to disconnect the dynamo M from operating as a motor and connect it for operating as a generator to supply a boosting current to the field winding GF of the main generator.

It will beassumed that this operation caused the car to stop at the oor but that it overruns the floor and the leveling apparatus now comes into operation to cause the car to level down to the floor at which the stop is to be made. The centering of the car switch not only deenergized the up direction relay U and applied the brake 5, but it also deenergized the retiring coil 35 by disconnecting the contact members 38 and thereby prepared the car for leveling if necessary. The deenergization of the coil 35 permitted the leveling levers 38 and 33 to move intoposition to engage the earn 3l if the car Stopped out of alinement with the floors.

Inasmuch as the car overran the floor, the down leveling lever 33 is engaged by the cam 3l and closes its contact members LS2, thereby energizing Athe down direction switch D by a circuit extending frorn supply conductor L+ through 43, LS2, D, L direction switch D closes its contact members DI thereby releasing the brake 5 from the hoisting drum and closes its contact members D2 and D3, thereby energizing the eld winding GF for -down direction operation. Atthe same time the down direction switch D closed its contact members D4, thereby energizing the field forcing con-` necting relay T which now opens its contact members T2 `and closes its contact members TI. The opening of the contact members T2 disconnects the dynamo M from the supply conductors L+ and L andthe closing of Jthecontact members TI connects it with the auxiliary field The energized down ving relay X. Inasmuch as the direction preference relay PU is energized and the direction preference relay PD is deenergized, no circuit is completed at this time for energizing the relay X. Hence the contact members XI remain closed in the circuit from the motor M to the windings GF. This prevents the resistor r2 from having any eil'ect on the boosting current of the dynamo M and thereby allows the full force of the boosting current to be supplied to the iield winding GF. Hence it is again seen that the relay X and its manner of connection provide means for compensating for the residual magnetism in the generator, because in this special instance the generator was being reversed while in the previous instance the generator was merely being started in the same direction. Obviously, upon being reversed, vthe generator needed the full forcing current that is now provided by the system.

As the rotation of the dynamo M during its action as a generator dies down, its voltage decreases and when it falls to around 20 volts, the regulating relay R becomes vdeenergized and thereby eil'ects disconnection of the motor M from the generator neld and reconnection of it across the control circuit conductors L+ and L. The deenergization of the relay R opens its contact members R2 thereby deenergizing the resetting relay S which opens its contact members BI and thereby deenergizes the connecting relay T. 'Ihe deenergised relay T opens its contact members TI thereby disconnecting the dynamo M from the generator ileld GF and closes its contact members T2 thereby connecting the motor M across the supply conductors L+ and L-andagaincausingittoidleatfullspeed. ready for the next forcing operation.

'Ihe closing of the contact members T! also again energized the regulating relay R to close its contact members R2 to again energize the resetting relay S. The energized relay S closes its contact members B2 thereby providing a self holding circuit for itself to beep it in condition for preparing the connecting relay T for energization in the next starting operation.

As the car moves downwardly under the control of the leveling apparatus, the lever I) slides oil' the cam 3| and is thereby operated to open its contact members ISI. 'lhis deenergises the down direction switch D which opens its contact members D2 and D! and thereby eilects the stopping of the car level with the floor. It may be observed here that the landing apparatus usually compensates for a very short distance. sayfromltoincheawhenthecardoesnot f land exactly level with the door. Therefore, it

thecardowntoaloweriloor. Thecarattendant throws the car switch C8 in its clockwise direction thereby engaging the contact members 22 and 24 successively, thus first energizing the down direction switch D and next the high speed relay V. '111e operation of the switch D and the relay v closes their contact members DI and DI and Vl thereby eifecting the starting of the car downwardly ihrough the energixation of the iield winding GF oi the generator G. At the same time the engagement of the contact members Il by the car switch C8 energizes the retiring coil ll to withdraw the leveling levers to keep themfromstrikinganycamsuntilthecaris to be stopped at some iloor.`

As the car starts downwardly after its down leveling operation, the dynamo M and the relays associated therewith operate to provide a boosting current for the generator neld GP through the resistor r2 thereby giving a reduced boosting current. 'Ihis is eifective because the energization of the down direction switch D closes contact members Dl thereby energizing the connectingrelayT. 'lheenergisedrelayTopens its contact members T! thus disconnecting the motor M from the supply conductors L+ and L- and closes its contact members Ti thus connecting the amature of the dynamo M to the generator ileld Gl'I through the resistor R2. The dynamo M, which has been running as a motor, now operates, by reason of its inertia. as a generator and provides a boosting current for the generator field GF to reduce the time required to get the car under way.

As the speed ci' the dynamo M drops, its voltage falls and, when it falls to about volts, the regulating relay R becomes deenergized and opens its contact members R2 thereby deenergizing the resetting relay B which, in turn, opens its contact members Si and deenergiaes the connecting relay T. The deenergized connecting relay T now opens its contact members Tl thus disconnecting the motor M from the generator heid GF, and closes its contact members T! thereby reconnecting the amature of the dynamo M and the regulating relay R to the supply conduc tors L+ andL-. TheenergixedrelayRisnow conditioned for again eifecting the disconnection ofthearmatureofthedynamoMi'romthegenerator neld GF thev next time it operates as a pensating eil'ect on the boosting current which restricts its value t0 the value suitable for boosting the generator when it is resuming operation in the same direction.

As the car approaches the iioor desired by the passenger, the car attendant centers theV car switch CS thereby deenergizing the high speed relay V to close its contact members Vl and thus reduce the speed of the car, and to also deenergize the switch D to eilect the stopping of the car at the floor desired. It will be assumed that at this iioor the car does not overrun or underrun but stops levelwith the desired iioor and, therefore, that no leveling operation is necessary.

By reason of the foregoing description, it will be seen that the apparatus is arranged for eiecting a smooth operation of a variable voltage system and provides a means for giving a boosting current to the generator iield at the instant the motor is to be started, and' that this boosting current is given lregardless of whether the car is starting on an ordinary run or whether it is starting in a leveling operation. It will also be seen that the'circuits and apparatus provide for so controlling the amount of the boosting current that the generator iieldwill receive a larger boosting current when its vdirection of operation is vbeing reversed than when it is being started in the same direction as that in which it has been operating.

Although the invention has been disclosed in connection with a variable voltage system for an elevator, it will be readily understood it may be oi value in many other installations of variable voltage systems; for instance, it will prove of considerable value in connection with the op eration of planers and in connection with the operation of many hoists as well as in connection with other machinery and apparatus.

Although I have illustrated and described only one specific embodiment oi my invention, it is to be understood that many modiiications thereoi and changes therein may be made without departing from the spirit and scope thereof.,

I claim as my invention:

1. In an electric system, a generator provided with means including a field winding for exciting the same, a dynamo-electric machine, means for connecting the dynamo-electric machine to a source of electric power for operation as a motor when said iield winding is .deenergized and for disconnecting it from said power" and electrically connecting it to said ileld winding for operation as a generator when said iield winding is being excited.

2. In an electric system, a generator provided with a field winding, means for connecting the generator ileld winding to a source of electric energy for building up the excitation of the field winding at a predetermined rate, a dynamo-electric machine, means for electrically connecting the dynamo-electric machine to a source of power for rotating it as a motor, and means responsive to operation of the iield winding connect-s f ing means for electrically disconnecting the dynamo-electric machine from its source of power and for electrically connecting it to said field winding whereby the inertia of said machine will cause it to act as a generator to deliver eleotrical energy to said i'leld winding for increasing the rate of excitation during the building up g period.

3. In an electric system, a generator provided with a field winding, means for connecting the generator eld winding to a source of electric energy for building up the excitation of the iield winding at a predetermined rate, a dynamo-electric machine, means for electrically connecting the dynamo-electric machine to a source of power for rotating it as a motor, means responsive to 'operation ofthe field winding connecting means for electrically disconnecting the dynamo-electric machine from its source of power and for electrically connecting it to said eld winding whereby the inertia of said machine will cause it to act as a generator to deliver electrical energy to said eld winding for increasing the rateo! excitation during the building up period, and means responsive to deceleration of the dynamoelectric machine while it isacting as a generator for electrically disconnecting it from said iield winding.

4. In an electric system, a generator provided with a iield winding, means for connecting the generator iield winding to a source of electric energy for building up the excitation of the iield winding at a predetermined rate, a dynamo-electric machine, means for electrically connecting the dynamo-electric machine to a source oi power for rotating it as a motor, means responsive to operation ci the field winding connecting means for electrically disconnecting the dynamo-electric machine from its source of power and for electrically connecting it to said ileld winding whereby the inertia o i said machine will cause it to act as a generator `to deliver electrical energy to said field winding for increasing the rate of excitation during the building up period, means responsive winding at a predetermined rate, a dynamo-electric machine having an armature and a field winding, means for electrically connecting the armature and neld winding of the dynamo-electric machine to a source of power for operating it as a motor, means responsive to operation of the connecting means of the generator field winding for disconnecting the armature of the dynamo-electric machine from its source of power and connecting it to the generator iield winding whereby the inertia of the dynamo-electric machine will cause it to act as a generator for boosting the starting ci? the generator, a device responsive toa predetermined decrease in voltage of the dynamo-electric machine while operating as a generator for disconnecting said armature from the generator rleld, and means responsive to operation of the voltage responsive device for reconnecting the armature to its source of power to cause the machine to resume operation as a motor.

e 6. In an elevator system, a generator provided with a iield winding, means for connecting the field winding to a source of electric energy for building up the excitation of the field winding at a predetermined rate, a dynamo-electric machine, means responsive tooperation of the connecting means for effecting operation of the dynamoelectric machine for delivering electric energy to energy delivered from said dynamo-electric machine tosaid neld winding in accordance with the direction in which said generator is energized after being deenergined.

'1.Inanelectricsystem, ageneratorprovlded with means including a iield winding for exciting the same, a dynamo-electric machine, means torconnectingthedynamo-eleetricmachine toa source ci electric power i'or operation as a motor whensaldiieldwindingisdeenerginedandfor disconnecting it from said power and electrically connecting it to said ileld winding for operation asageneratorwhensaideldwindingisbeing excited, and means responsive to the direction of energization of the generator for controlling the amount oi' energy delivered by said dynamo-elecltrlcmachineoperatingasage'neratortosiiid buildinguptbeencitationoitheiieldwindingat apredeterminedrate,acontrolsyltemforsaid generatonamachinelnvlngan armatureandaiieldwindlngarettimrelay responsivetoaninoperatedcmditionoithecontrol system for the machine to a source ci' 'power for operating it as a motor, a iield iorcing relay responsive to operation oi.' the control system in starting the generator for disconnecting the armature o! the machine from its source of power and electrically connecting it to the generator field winding for increasing said predetermined rate of excitation of the generator held winding, a voltage relay responsive to a predetermined drop in the voltage oi the machine operating as a generator for operating said resetting relay, means responsive to operation oi the resetting relay lor operating the ileld forcing relay, means responsive to the operation of the iieid forcing-relay for disconnecting the machine amature from the generator ileld and reconnecting it to its source oi power whereby the ma. chine again operates as a motor, a plurality of direction relays responsive to the direction of energintlon of the generator, a resistance element anociatedwiththecircuiti'orconnectingtbe armature to the generator held. and a residual w relay responsive to operation o! the direction relays and the control means tor connecting the resistor in circuit between the amature and generato!l ileld when the generator iabeingenergizedin thesamedirection ofoperation in which it has been energized and for eliminating the elect oi' the resistor in the circuit between the amature and the generator ield when the generator is being energized in a direction opposite to the direction in which it has been energized.

l0. In an electric system, a generator provided with a ileld winding for exciting it, control means for connecting the iield winding to a source of power to start excitation, a dynamo-electric machine, means i'or connecting the machine to a source of power to piace it in operation before operation oi' said control means, and means responsive to operation oi' the control means for disconnecting the machine from its source of power and electrically connecting it to said ileld winding ior operation as a generator when excitation of said field winding is started.

11. In an electric system, a generator having a neld winding lor energizing said generator, means for controlling the direction and amount of gaies-atar iield an amount o! energy diiierent from said predetermined amount.

WILLIAM F. EAMES. 

